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Sophos Free A-V For Mac May Kill Time Machine Backups
kdawson writes "Herewith the tale of the instantaneous loss of 19 months of Time Machine backup data, with the possible involvement of a fresh install of Sophos's new
free Mac A-V package. Sophos support has been contacted but has not responded as of this writing."
It isn't their first Mac app. They've been selling it to businesses before now, but businesses don't generally use Time machine, and would never execute a deletion command using an antivirus on a backup archive while it was running. Not sure whether this is an OS bug, or a sophos bug, or whether if he had allowed the command to finish, it would have worked fine. (Maybe it was just taking a long time.) --Sam
No, it's separate files. You can browse it using finder or terminal.
Unless you're backing up a filevault protected home directory. Then it handles it in just about the stupidest way possible: it saves the whole honking encrypted image as one big file.* And despite the fact that it doesn't decrypt the image, it still only works if you're logged in and the image is open.
*If you're set up as sparse images, then you do a little better. But still, no incremental backups for you. If a file changes, you have to copy the *whole* thing, because good encryption won't make it obvious which bits of the file are different. Also, I'm not sure it can tell which files are, say, disk cache for the browser....
Can you be Even More Awesome?!
FYI, I'm not using filevault, just individual files to be backed up... but TM uses sparsebundles in ways I don't begin to understand. One respondent via Twitter suggested that Sophos may have simply been in the process of deleting the entire sparsebundle -- i.e. the entire lot of backups -- when I killed its process. No idea if this is correct. I hope Sophos eventually provides some insight.
yes, one large file which is actually a sparse disk image.
it's a sparse disk image bundle thingy. Which uses a bunch of 8MB files, not one file. from the hdiutil man page:
By default, UDSP images grow one megabyte at a time.
Introduced in 10.5, UDSB images use 8 MB band files
which grow as they are written to.. -imagekey
sparse-band-size=size can be used to specify the
number of 512-byte sectors that will be added each
time the image grows. Valid values for SPARSEBUNDLE
range from 2048 to 262144 sectors (1 MB to 128 MB).
The maximum size of a SPARSE image is 128 petabytes;
the maximum for SPARSEBUNDLE is just under 8
exabytes (2^63 - 512 bytes minus 1 byte). The
amount of data that can be stored in either type of
sparse image is additionally bounded by the filesys-
tem in the image and by any partition map. compact
can reclaim unused bands in sparse images backing
HFS+ filesystems. resize will only change the vir-
tual size of a sparse image. See also USING PERSIS-
TENT SPARSE IMAGES below.
One thing. directly connected hard drives do not use sparse bundles if FileVault is not on,.
The time machine stores the back up files on an external hard drive in a specific way such that can perform the backup task and the possible restore task effectively. In order to this to work noone should modify or delete any data stored in the backup location. This will most likely corrupt the backup.
The author of the article told Sophos AV to delete files from within the time machnien backup location ... well, of course one can expect that it messes things up.